A transmission of a vehicle such as a motorcycle includes a main shaft and a drive shaft, each of which is provided with a plurality of gears. Further, the transmission includes a shift device that switches the gears according to a shift operation of a shift pedal.
The shift device includes a shift cam, a shift fork, or the like. The shift cam rotates according to the shift operation. A cam groove is formed at an outer circumferential surface of the shift cam, and a part of the shift fork is engaged with the cam groove. When the shift cam rotates, the cam groove causes the shift fork to move along the main shaft or the drive shaft. Due to the movement of the shift fork, a specific gear of the plurality of gears provided on the main shaft or the drive shaft slides. Accordingly, among the plurality of gears supported by the main shaft and the drive shaft, a combination of gears for transmitting rotation of the main shaft to the drive shaft is switched, and thus a gear ratio changes.
Such a shift device includes an angle sensor that detects a rotation angle of the shift cam. For example, a transmission described in JP-A-2016-70357 below includes a main shaft in which a plurality of driving gears are supported, a counter shaft in which a plurality of driven gears meshing with the plurality of driving gears are supported, a shift fork that is engaged with a shifter gear including the driving gears and the driven gears, a shift drum in which a lead groove is formed at an outer circumferential surface and one end of the shift fork is engaged with the lead groove, a sensor shaft that is provided on the shift drum and rotates integrally with the shift drum, and an angle sensor that detects a rotation angle of the sensor shaft. Incidentally, the shift drum has the same function as the shift cam.
In the transmission of JP-A-2016-70357, the sensor shaft and the shift drum are disposed coaxially, and an end portion of the sensor shaft is fixed to an end portion of the shift drum with a nut. Accordingly, the sensor shaft rotates integrally with the shift drum. The angle sensor is a potentiometer, and outputs a voltage based on the rotation angle of the sensor shaft.